PRESSURE SENSITIVE ADHESIVE ITEM

Abstract

A pressure-sensitive adhesive article is provided comprising (a) a substrate (Sa), (b) in contact with the substrate (Sa), a layer (Lb) of a pressure-sensitive composition (Cb) comprising one or more acrylic polymers (POLb) having a Tg of 20°C or lower, and (c) in contact with the layer (Lb), a layer (Lc) comprising (i) one or more acrylic polymers (POLc1) having a Tg of 20°C or lower, and (ii) one or more acrylic tackifying agent polymers having a Tg of -10°C or higher. A method for manufacturing the pressure-sensitive adhesive article and an adhered article manufactured using the pressure-sensitive adhesive article are also provided.

Description

Pressure-sensitive adhesives (PSAs) containing acrylic polymers have many desirable characteristics. For example, they generally have better resistance to chemical reagents and UV light than PSAs made from many other materials. It is often desirable to provide an acrylic PSA that adheres well to polyolefin target substrates. In the past, a tackifying agent compound was sometimes added to PSA to increase the tackiness (also called adhesion or stickiness) of the PSA to a target substrate. However, the addition of a tackifying agent typically results in an undesirable reduction in the shear strength of the PSA. US 9,765,241 describes a pressure-sensitive adhesive article comprising a substrate, a layer containing an acrylic polymer, and a layer containing an acrylic polymer comprising polymerized units of one or more high-aliphatic vinyl monomers. It is advisable to provide a PSA containing acrylic polymer and which, when bonded to polyolefin target substrates, exhibits both good tackiness and good shear strength. nfrRznn / zznz / E / YiAi Ref. 332536 Furthermore, it is advantageous to provide a PSA comprising layers, where the top layer (i.e., the layer adjacent to the target substrate) contains a relatively high level of tackifying agent and the other layers contain a relatively low level of tackifying agent. It is currently anticipated that, in such a multilayer PSA, if the tackifying agent were to migrate from the top layer into the other layers, the tackiness of the adhesion to the target substrate would be reduced. Therefore, it is also advantageous to provide a multilayer PSA that resists the migration of tackifying agent from the top layer. BRIEF DESCRIPTION OF THE INVENTION The following is a statement of the invention. A first aspect of the present invention is a pressure-sensitive adhesive article comprising (a) a substrate (Sa), (b) in contact with the substrate (Sa), a layer (Lb) of a pressure-sensitive composition (Cb) comprising one or more acrylic polymers (POLb) having a Tg of 20°C or less, and (c) in contact with the layer (Lb), a layer (Le) comprising, by weight as a function of the weight of layer (Le), (i) from 60% to 99.5% of one or more acrylic polymers (POLcl) having a Tg of 20°C or less, and (ii) from 0.5% to 40% of one or more acrylic polymers (POLc2) having a number-average molecular weight of 2,000 or greater, having a number-average molecular weight of 35,000 or less, having a Tq of -10°C or higher, and comprising polymerized units, by weight as a function of the weight of (POLc2), (A) from 50% to 99.(B) 9% of one or more unsubstituted alkyl esters of (meth)acylglycerol acid, wherein the alkyl group has from 1 to 20 carbon atoms, (C) 0% to 50% of acrylic acid, methacrylic acid or a mixture thereof, and 0% to 50% of one or more additional vinyl monomers. A second aspect of the present invention is a method for manufacturing the pressure-sensitive article of the first aspect, wherein the method comprises, (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of the acrylic polymer (POLb) on a first surface, (B) forming a layer of an aqueous composition (Qc) containing dispersed particles containing (i) the acrylic polymer (POLcl) and (ii) the acrylic polymer (POLc2) on a second surface, (C) drying the layer of the aqueous composition (Qb) to form the layer (Lb), and (D) drying the layer of the aqueous composition (Qc) to form the layer (Le). A third aspect of the present invention is an adhered article made by a process of bringing a substrate (Sd) into contact with the article of the first aspect, wherein the substrate (Sd) is in contact with the layer (Le). BRIEF DESCRIPTION OF THE FIGURES The following is a brief description of the figures. Figure 1 is a vertical cross-section of a pressure-sensitive adhesive article of the present invention showing the substrate (Sa) (1); a layer (Lb) (2) of a composition (Cb) containing one or more acrylic polymers (POLb); and a layer (Le) (3) of a composition (Ce) containing the polymer (POLcl) and the polymer (POLc2). Figure 1 is not drawn to scale in any respect. For example, the size of the pressure-sensitive adhesive article of the present invention in the horizontal direction shown in Figure 1 may be larger by a factor of 1,000 or more than the size in the vertical direction shown in Figure 1. Figure 2 (also not drawn to scale) represents a preferred use in which the pressure-sensitive adhesive article of the present invention can be placed. Figure 2 shows the layer (Le) (3) in contact with an additional substrate (Sd) (4). DETAILED DESCRIPTION OF THE INVENTION The following is a detailed description of the invention. As used herein, the following terms have the designated definitions, unless the context clearly indicates otherwise. As used herein, dynamic mechanical analysis (DMA) refers to measurements made on shear geometry in the linear viscoelastic range at a frequency of 1 s⁻¹. DMA measures the elastic modulus (G'), the loss modulus (G), and the tandelta. The elastic modulus is reported herein in kilopascals (kPa). The glass transition temperature (Tg) of a material is determined by differential scanning calorimetry using the midpoint method and a temperature sweep rate of 10 °C per minute in accordance with test method ASTM D7426-08 (American Society of Testing and Materials, Conshohocken, Pa., USA). As used herein, a polymer is a relatively large molecule formed from the reaction products of smaller repeating chemical units. Polymers can have structures that are linear, branched, star-shaped, looped, hyperbranched, cross-linked, or a combination thereof; Polymers can have only one type of repeating unit (homopolymers) or they can have more than one type of repeating unit (copolymers). Copolymers can have the various types of repeating units arranged randomly, sequentially, in blocks, in other arrangements, or in any mixture or combination thereof. The size of polymers is characterized by Mn, the number-average molecular weight, or by Mw, the weight-average molecular weight, both measured by size-exclusion chromatography. As used herein, polymer weight means the dry weight of the polymer. Molecules that can react with each other to form the repeating units of a polymer are known herein as monomers. The repeating units thus formed are known herein as polymerized units of the monomer. Vinyl monomers have the structure R2R3 ηΐτβζηη / ζζηζ / Ε / γίΛΐ where each of R1, R2, R3, and R4 is, independently, a hydrogen, a halogen, an aliphatic group (such as, for example, an alkyl group), a substituted aliphatic group, an aryl group, a substituted aryl group, another substituted or unsubstituted organic group, or any combination thereof. Alkyl groups can be linear, branched, cyclic, or any combination of these. Suitable vinyl monomers include, for example, styrene, substituted styrenes, dienes, ethylene, other alkenes, dienes, ethylene derivatives, and mixtures thereof. Ethylene derivatives include, for example, substituted or unsubstituted versions of the following: ethenyl esters of substituted or unsubstituted alkanoic acids (including, for example, vinyl acetate and vinyl neodecanoate), acrylonitrile, (meth)acrylic acid, (meth)acrylates, (meth)acrylamides, vinyl chloride, halogenated alkenes, and mixtures thereof. As used herein, (meth)acrylic means acrylic or methacrylic; (meth)acrylate means acrylate or methacrylate; and (meth)acrylamide means acrylamide or methacrylamide. The term substituted refers to having at least one chemical group attached, such as, for example, an alkyl group, alguenyl group, vinyl group, hydroxyl group, carboxylic acid group, other functional groups, and combinations thereof.In some forms, substituted monomers include, for example, monomers with more than one carbon-carbon double bond, monomers with hydroxyl groups, monomers with other functional groups, and monomers with combinations of functional groups. (Meth)acrylates are substituted and unsubstituted esters or amides of (meth)acrylic acid. As used herein, acrylic monomers are selected monomers of (meth)acrylic acid, aliphatic esters of (meth)acrylic acid, aliphatic esters of (meth)acrylic acid having one or more substituents on the aliphatic group, (meth)acrylamide, N-substituted (meth)acrylamide, and mixtures thereof. As used herein, vinylaromatic monomers are selected monomers of styrene, alpha-alkyl styrenes, other substituted styrenes, and mixtures thereof. As used herein, an acrylic polymer is a polymer in which 50% or more of the polymerized units are acrylic monomers, and also in which 70% or more of the polymerized units are acrylic monomers or vinyl aromatic monomers. The percentages are by weight based on the weight of the polymer. As used herein, a chain transfer agent is a substance that acts during the free-radical polymerization of vinyl to transfer a radical from a growing polymer chain to a non-radical molecule. The molecule receiving the radical may be the chain transfer agent itself. As used herein, a tackifying agent is an organic compound having a molecular weight of 500 to 50,000 and having a glass transition temperature of 10°C or higher. A pressure-sensitive adhesive (PSA) is an adhesive that forms a bond with a substrate when pressure is applied to bring the adhesive and substrate into contact. The bond forms without the addition of any additional materials or the application of heat. As used herein, a pressure-sensitive adhesive article is an article in which a pressure-sensitive adhesive is bonded to a first substrate and in which a surface of the PSA (the available surface) is available to make contact with a second substrate. The available surface of the PSA may or may not be in contact with a release material. A release material is a material that forms a weak bond with the PSA and can be easily removed to expose the available surface. In the present, a composition is considered aqueous if the composition contains water in an amount of 25% or more by weight based on the weight of the composition. It is stated herein that particles are dispersed in a liquid medium if the particles are distributed throughout the liquid medium; the dispersed particles may form an emulsion, a latex, a dispersion, a suspension, or some other composition in which the particles are dispersed in a liquid medium. A liquid medium is considered herein to be an aqueous medium if water constitutes 50% or more by weight of the liquid medium (excluding the weight of the dispersed particles). When it is stated herein that an aqueous composition is dried, it means that the composition is allowed to dry under ambient conditions or is dried by the application of heat, exposure to moving gas (which may or may not be heated), or a combination of these. The relationships presented herein are characterized as follows. For example, if a relationship is described as 3:1 or greater, it could be 3:1, 5:1, or 100:1, but it cannot be 2:1. This characterization can be expressed more generally as follows. When a relationship is described herein as X:1 or greater, it means that the relationship is Y:1, where Y is greater than or equal to X. For another example, if a relationship is described as 15:1 or less, it could be 15:1, 10:1, or 0.1:1, but it cannot be 20:1. Generally speaking, when a relationship is described herein as W:1 or less, it means that the relationship is Z:1, where Z is less than or equal to W. The present invention involves the use of a substrate, hereinafter referred to as substrate (Sa). The substrate (Sa) can be any material. Paper, polymer film, and metal foil are preferred. Among polymer films, polyester films are preferred. Among polymer films, those in which at least one side has been treated by corona discharge are preferred. In contact with the substrate (Sa) is a layer of a composition, herein referred to as composition (Cb). Composition (Cb) contains one or more polymers, herein referred to as polymer (POLb). Polymer (POLb) has a glass transition temperature (Tg) of 20°C or lower; preferably 10°C or lower. Preferably, polymer (POLb) has a glass transition temperature (Tg) of -100°C or higher. Preferably, the composition (Cb) has little or no tackifying agent. That is, the amount of tackifying agent in the composition (Cb), by weight as a function of the dry weight of the composition (Cb), is less than 10%; more preferably 3% or less; more preferably 1% or less; more preferably zero. Preferably, the polymer (POLb) is an acrylic polymer. Preferably, the amount of polymerized acrylic monomer units in the polymer (POLb) is, by weight of the polymer (POLb), 50% or more; more preferably 70% or more; more preferably 90% or more; more preferably 99% or more. Preferably, the polymer (POLb) has an Mw of 10,000 or greater; more preferably 50,000 or greater. Preferably, the polymer (POLb) contains polymerized units of one or more of n-butyl acrylate (n-BA), ethyl acrylate (EA), isooctyl acrylate (i-OA), or a mixture thereof. As used herein, isooctyl is an unsubstituted alkyl group containing exactly 8 carbon atoms in a branched configuration. The term isooctyl includes all branched isomers of 8-carbon alkyl groups and all mixtures of such isomers, including, for example, the 2-ethylhexyl group, dimethylhexyl groups, methylheptyl groups, trimethylpentyl groups, and mixtures thereof. Preferably, the sum of the amounts of polymerized n-BA units, polymerized EA units, and polymerized i-OA units in polymer (POLb), by weight as a function of the weight of polymer (POLb), is 50% or more. with greater preference 75% or more; with greater preference 90% or more. Preferably, each polymer in the composition (Cb) that has an Mw of 10,000 or greater is an acrylic polymer. Preferably, the amount of polymer (POLb) in the composition (Cb) , by weight as a function of the dry weight of the composition (Cb) , is 80% or more; more preferably 90% or more; more preferably 95% or more. Preferably, composition (Cb) has the properties of a PSA. Preferably, composition (Cb) nfrRznn / zznz / E / YiAi has an elastic modulus (G') of 20 kPa or greater over a temperature range including 10°C to 40°C. Preferably, composition (Cb) has an elastic modulus (G') of 1,000 kPa or less over a temperature range including 10°C to 40°C; more preferably 500 kPa or less. Preferably, the composition (Cb) is in contact with a substrate surface (Sa) that has been treated by corona discharge. A layer (Le) of composition (Ce) is in contact with the layer (Lb) of composition (Cb). Composition (Ce) contains one or more polymers (POLcl). The required and preferred characteristics of the polymer (POLcl) are the same as those described above for the polymer (POLb). The polymers (POLb) and (POLcl) may be the same or different. Preferably, the amount of (POLcl) in composition (Ce), by weight as a function of the weight of composition (Cb), is 70% or more; more preferably 80% or more; more preferably 85% or more. Preferably, the amount of (POLcl) in composition (Ce), by weight as a function of composition (Cb), is 99.5% or less; more preferably 99% or less; more preferably 98% or less; more preferably 95% or less. with greater preference 91% or less. The composition (Ce) further contains acrylic polymer (POLc2). The acrylic polymer (POLc2) has a number-average molecular weight (Mn) of 2,000 or greater. The acrylic polymer (POLc2) has an Mn of 35,000 or less. The acrylic polymer (POLc2) has a glass transition temperature (Tg) of -10°C or greater; more preferably 0°C or greater; more preferably 10°C or greater. Preferably, the Tg of the acrylic polymer (POLc2) is greater than the Tg of the acrylic polymer (POLcl). Preferably, the difference between the Tg of the acrylic polymer (POLc2) and the Tg of the acrylic polymer (POLcl) is 10°C or greater; more preferably 20°C or greater; more preferably 50°C or greater. The acrylic polymer (POLc2) contains polymerized units of one or more acrylic monomers herein labelled as monomer (MON-A). The monomer (MON-A) is an unsubstituted alkyl ester of (meth)acrylic acid. The number of carbon atoms in the alkyl ester group of the monomer (MON-A) is 1 or more; preferably 2 or more; more preferably 3 or more. The number of carbon atoms in the alkyl ester group in the monomer (MON-A) is 20 or fewer; more preferably 10 or fewer; more preferably 8 or fewer. The amount of polymerized units of the monomer (MON-A) in the acrylic polymer (POLc2), by weight as a function of the weight of the acrylic polymer (POLc2), is 50% or more; more preferably 75% or more; more preferably 85% or more; more preferably 95% or more. with greater preference 99% or more. The amount of polymerized monomer units (MON-A) in the acrylic polymer (POLc2) is, by weight as a function of the weight of the acrylic polymer (POLc2), 99.9% or less; with greater preference 99.8% or less; with greater preference 99.6% or less. The acrylic polymer (POLc2) optionally contains polymerized units of one or more acrylic monomers, herein labelled as monomer (MON-B). The monomer (MONB) is selected from acrylic acid, methacrylic acid, and mixtures thereof. When present, the amount of polymerized monomer units (MON-B) in the acrylic polymer (POLc2), by weight as a function of the weight of the acrylic polymer (POLc2), is 0.1% or more; more preferably 0.2% or more; more preferably 0.4% or more. The amount of polymerized monomer units (MON-A) in the acrylic polymer (POLc2), by weight as a function of the weight of the acrylic polymer (POLc2), is 50% or less; more preferably 25% or less; more preferably 15% or less; more preferably 5% or less; more preferably 1% or less. The acrylic polymer (POLc2) optionally contains polymerized units of one or more acrylic monomers herein labelled as monomer (MON-C). Monomer (MONO) is any vinyl monomer, except that monomer (MON-C) is different from monomers (MON-A) and (MON-B). The amount of polymerized monomer (MON-A) units in the acrylic polymer (POLc2), by weight as a function of the weight of the acrylic polymer (POLc2), is 50% or less; more preferably 10% or less; more preferably 2% or less. The amount of polymerized monomer (MON-B) units in the acrylic polymer (POLc2) may be zero. Acrylic polymer (POLc2) can be manufactured by any method. In a preferred method, polymerization to form acrylic polymer (POLc2) is carried out in the presence of one or more chain transfer agents. Preferably, the amount of chain transfer agent, by weight as a function of the total weight of the monomers used in the formation of acrylic polymer (POLc2), is 1% or more; more preferably 2% or more; more preferably 4% or more. Preferably, the amount of chain transfer agent, by weight as a function of the total weight of the monomers used in the formation of acrylic polymer (POLc2), is 10% or less; more preferably 8% or less; more preferably 6% or less. The preferred chain transfer agents have one or more SH groups attached.The preferred chain transfer agents also have a linear chain of n adjacent carbon atoms, where n is 2 or more; most preferably 4 or more; most preferably 6 or more. Preferably, the amount of acrylic polymer (POLc2) in the composition (Ce), by weight as a function of the weight of the composition (Ce), is 30% or less; more preferably 20% or less; more preferably 15% or less. Preferably, the amount of acrylic polymer (POLc2) in the composition (Ce), by weight as a function of the weight of the composition (Ce), is 0.5% or more; more preferably 1% or more; more preferably 2% or more; more preferably 5% or more; more preferably 9% or more. Preferably, the composition (Ce) has the properties of a PSA. Preferably, the composition (Ce) has an elastic modulus (G') over a temperature range including 10°C to 40°C of 5 kPa or greater; more preferably 10 kPa or greater; more preferably 20 kPa or greater. Preferably, the composition (Ce) has an elastic modulus (G') over a temperature range including 10°C to 40°C of 1000 kPa or less; more preferably 500 kPa or less. Preferably, the composition (Ce) contains little or no tackifier other than an acrylic polymer. That is, preferably, the amount of tackifier that is not an acrylic polymer in the composition (Ce) is, by weight as a function of the dry weight of the composition (Ce), less than 10%; more preferably 3% or less; more preferably 1% or less; more preferably zero. It is useful to consider the quantity (SUMc), defined herein as the sum of the polymer weight (POLcl) and the polymer weight (POLc2). Preferably, the ratio between the quantity (SUMc) and the total composition weight (Ce) is 0.6:1 or greater; more preferably 0.8:1 or greater; more preferably 0.9:1 or greater. It is useful for characterizing the total thickness (TOT), which is the sum of the layer thickness (Lb) plus the layer thickness (Le). Preferably, the total thickness (TOT) is 1 micrometer or more; more preferably 2 micrometers or more; more preferably 5 micrometers or more. Preferably, the total thickness (TOT) is 50 micrometers or less; more preferably 40 micrometers or less. The layers (Lb) and (Le) can be characterized by their coating weight, which is the weight of dry material per unit area. Preferably, the ratio of the coating weight of layer (Lb) to the coating weight of layer (Le) is 0.1:1 or greater; more preferably 0.25:1 or greater; more preferably 0.67:1 or greater. Preferably, the ratio of the coating weight of layer (Lb) to the coating weight of layer (Le) is 9:1 or less; more preferably 4:1 or less; more preferably 1.5:1 or less. In some embodiments, the pressure-sensitive article of the present invention has a release coating in contact with the layer (Le). A release coating has a low-energy-density surface, such as, for example, a silicone coating, to which a PSA does not normally adhere well. When present, the release coating protects the layer (Le) of the pressure-sensitive article of the present invention until it is convenient to use the pressure-sensitive article of the present invention by adhering it to a substrate of interest (i.e., the substrate (Sd)). The release coating can be easily removed from the pressure-sensitive article of the present invention, which can then be brought into contact with the substrate (Sd). The pressure-sensitive article of the present invention can be manufactured by any method. In a preferred method, each of the layers (Lb) and (Le) is constructed by forming a layer of an aqueous composition and then drying that aqueous composition layer. Preferably, the layer (Lb) is formed by first providing an aqueous composition (AQb) containing dispersed particles of acrylic polymer (POLb). The aqueous composition (AQb) may contain additional compounds besides water and the acrylic polymer (POLb). A preferred method for preparing an aqueous composition (AQb) is to carry out an aqueous emulsion polymerization to form dispersed particles of aqueous polymer (POLb) in the form of a polymer latex, which can then serve as the aqueous composition (AQb). Preferably, the dispersed polymer particles in the aqueous composition (AQb) have a volume-average diameter of 50 to 750 nanometers. Preferably, the amount of acrylic polymer (POLb) present in the aqueous composition (AQb), by weight as a function of the total weight of the aqueous composition (AQb), is 20% to 55%. Similarly, a preferred method for preparing the layer (Le) is to provide a suitable aqueous composition (AQc), which is applied to the layer (Lb) and then dried. Preferably, the aqueous composition (AQc) contains dispersed polymer particles. In some embodiments, the dispersed polymer particles contain acrylic polymer (POLcl) and acrylic polymer (POLc2). In preferred embodiments, the aqueous composition (AQc) contains dispersed particles of acrylic polymer (POLcl) and also contains separate dispersed particles of acrylic polymer (POLc2). The aqueous dispersion (AQc) can be prepared by any method. In a preferred method, aqueous emulsion polymerization is carried out to produce a latex (hereinafter labelled (AQcl)) of acrylic polymer particles (POLcl) dispersed in an aqueous medium. The necessary and preferred characteristics of the aqueous composition (AQcl) are the same as those described above for the aqueous composition (AQb). In some embodiments, a separate aqueous composition (hereinafter labelled (AQc2)) containing polymer particles (POLc2) dispersed in an aqueous medium is provided, and the aqueous compositions (AQcl) and (AQc2) are blended to form an aqueous composition (AQc). In preferred embodiments (in situ embodiments), the acrylic polymer (POLc2) is formed by aqueous emulsion polymerization of one or more monomers in (AQcl).In in situ modes, the polymer (POLc2) that forms can be formed on top of the polymer particles (POLcl). In preferred in situ modes, polymer particles (POLc2) are formed that are separate from the polymer particles (POLcl). In in situ modes, one or more optional additional ingredients can be added to the polymer formation result (POLc2) in the presence of polymer (POLcl), and the result is used as an aqueous composition (AQc). The pressure-sensitive article of the present invention can be manufactured by any method. Preferably, the article is manufactured by a method comprising the following steps: (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of the acrylic polymer (POLb) on a first surface, (B) forming a layer of an aqueous composition (Qc) containing dispersed particles containing (i) the acrylic polymer (POLcl) and (ii) the acrylic polymer (POLc2) on a second surface, (C) drying the layer of the aqueous composition (Qb) to form layer (Lb), and (D) drying the layer of the aqueous composition (Qc) to form layer (Le). In some embodiments, both steps (A) and (B) are performed, and then steps (C) and (D) are performed simultaneously. In such embodiments, a layer (Lbl) of aqueous composition (Cbl) is applied to the substrate (Sa) (the first surface), and while the aqueous composition layer (Lbl) (Cbl) is still wet, a layer (Lcl) of aqueous composition (Ccl) is applied on top of the aqueous composition layer (Lbl) (Cbl) (the second surface), and then the entire assembly is dried. Among such embodiments, it is preferred that steps (A) and (B) be performed simultaneously. That is, a multi-layer coating device is used that simultaneously applies a layer (Lbl) of aqueous composition (Cbl) to the substrate (Sa) and also applies a layer (Lcl) of aqueous composition (Ccl) over the aqueous composition layer (Lbl) (Cbl), and then the entire assembly is dried. A suitable coating device is a slip coating machine.A slip coating machine forms a liquid compound in which there is a layer (Lbl) of aqueous composition (Cbl) beneath a layer (Lcl) of aqueous composition (Ca); while keeping those layers intact, the slip coating machine applies a layer of the entire compound onto a substrate (Sa) in a manner that puts the layer (Lbl) in contact with the substrate (Sa) and leaves the layer (Lcl) in contact with the air; the entire article is then dried to remove water from the aqueous compositions. Also contemplated are embodiments in which the pressure-sensitive article is manufactured by a transfer coating method, for example, a method involving manufacturing a coating layer of composition (Ce) onto a peelable coating (the second surface) and then manufacturing a coating layer of composition (Cb) on top of the composition layer (Cb) (the first surface), then contacting the composition layer (Cb) with the substrate (Sa) (preferably under pressure), and then removing the release coating. In such embodiments, step (B) is performed before step (A). It is envisaged that the pressure-sensitive adhesive article of the present invention will be used by bringing it into contact with an additional substrate (Sd), the target substrate. It is envisaged that pressure will be applied so that the composition (Ce) and the substrate (Sd) come into intimate contact and are then released. It is envisaged that the result will be an adhered article in which the pressure-sensitive adhesive article nfrRznn / zznz / E / YiAi is still intact and in which the composition (Ce) is adhered to the substrate (Sd). The substrate (Sd) can be any substance. Preferably, the substrate (Sd) is a polyolefin. The present invention is not limited to any specific mechanism. It is envisaged that tackiness arises from the interaction between the layer (Le) of the pressure-sensitive adhesive article of the present invention and the substrate surface (Sd) (i.e., the target substrate). It is envisaged that the pressure-sensitive article of the present invention will have acceptable tackiness because the acrylic polymer (POLc2) is envisaged to function as a tackifying agent in the layer (Le), which is in contact with the substrate (Sd). It is envisaged that the acrylic polymer (POLc2) will resist migration from layer (Le) to layer (Lb), thereby maintaining a high concentration of acrylic polymer (POLc2) in the layer (Le) (which will be in contact with the substrate (Sd)), and thus maintaining the ability to exert a relatively high tackiness on the substrate (Sd). In contrast to the present invention, it is envisaged that a comparative pressure-sensitive article, similar to the pressure-sensitive article of the present invention, could be manufactured, except that in the comparative article, the acrylic polymer (POLc2) is replaced by a previously known tackifying agent that is not an acrylic polymer, such as, for example, a rosin ester. It is expected that the rosin ester will migrate freely from the top layer (analogous to layer (Le)) to the other layers (analogous to layer (Lb)). Therefore, the full improvement in tack performance that might be expected would not be achieved, because the migration would cause the concentration of rosin ester in the top layer to decrease. The following are examples of the present invention. The operations were performed at room temperature (approximately 23°C) except where otherwise indicated. Preparatory Example 1 (PEI). The procedure for preparing an acrylic polymer that qualifies as acrylic polymer (POLc2) was as follows. A 3-liter, four-necked round-bottom flask was filled with 610 grams of water and ammonium persulfate (APS) at a level of 1.5 wt% based on the monomer. A monomer emulsion feed consisting of 280 grams of water, 100 grams of anionic sulfate surfactant, 1000 grams of monomer, and n-dodecyl mercaptan (n-DDM) (5 wt% based on the monomer) was then added uniformly to the flask over 3 hours while maintained at a polymerization temperature of 84°C. Simultaneously with the monomer emulsion feed, APS was added at a level of 0.5 wt% based on the monomer in 45 grams of water. After the addition of monomer, the batch was held at 84°C for 30 minutes, then cooled to 70°C and 1 gram of 28% aqueous ammonia was added.The batch was further cooled to room temperature and then filtered, and the polymer product was recovered. The monomer composition was 99.5% by weight of n-butyl methacrylate and 0.5% of methacrylic acid. Pressure-sensitive adhesive compositions were prepared as follows. All samples were lightly formulated with a wetting agent, such as 0.3%–0.5% (wt., wet / wet) of SURFYNOLITMI44 0 wetting agent obtained through Air Products (440) and 0.3%–0.5% (wt., wet / wet) of Solvay OT-75 Aerosol, depending on the total emulsion, to improve wetting for laboratory reductions unless otherwise specified. Viscosity was then adjusted to approximately 1000 mPa*s (1000 cps) (Brookfield, RVDV, 30 rpm, 63#) using a thickener from the ACRYSOL™ family of The Dow Chemical Company, Midland, Michigan. The laboratory reductions to form multilayer articles as shown in Figure 1 were performed as follows. Layer (Lb) (2) was coated onto a first silicone-coated paper or film release coating and then dried at 80°C for 5 minutes with a wet coating thickness between 2 and 50 micrometers. Separately, layer (Le) (3) was coated onto a second release coating, also dried at 80°C for 5 minutes with a wet coating thickness between 2 and 50 micrometers. The unbonded layer (i.e., layer (Lb)) was then transferred to a corona-treated polypropylene (PP) film (60 micrometers thick) by laminating the PP film (substrate (Sa) (1)) and coating the first release coating with adhesive. The first release liner was then removed to expose the unbonded adhesive layer (Lb).This layer (Lb) was then brought into contact with layer (Le) (currently coated over the second release liner) to form a laminate. The second release liner was then removed, resulting in the multilayer construction shown in Figure 1. Loop tack (PSTC 16 test method) (Pressure Sensitive Tape Council, One Parkview Plaza, Suite 800, Oakbrook Terrace, IL 60101, USA) was performed as follows. The loop tack test measures the initial adhesion when the adhesive comes into contact with the substrate (Sd) (4). The test was conducted after conditioning the adhesive laminate in a controlled environment (22.2 to 23.3°C (72 to 74°F), 50% relative humidity) for at least 1 day. A 2.54 cm (1 in.) wide strip was cut and folded into a loop, exposing the adhesive side. It was then placed between the jaws of the INSTRON tensile tester. <tm>The lower jaw was lowered at a rate of 12 in / min to the substrate so that a 2.54 cm x 2.54 cm (1 in x 1 in) square area of ​​the adhesive was in contact with the substrate (Sd) (4) for 1 second. The adhesive was then removed, and the peak force required to separate the adhesive from the substrate was recorded. The substrate (Sd) (4) was low-density polyethylene. Pressure-sensitive adhesive articles were also analyzed using secondary ion mass spectrometry (SIMS) with gas-assembly ion beam etching in depth profiling mode, which reveals the relative concentration of specific functional groups and molecular fragments as a function of depth. For samples containing rosin ester, the functional group studied was rosin acid, and for samples containing PEI acrylic polymer, the functional group studied was butyl alcohol. nfrRznn / zznz / E / YiAi The materials used in these examples were the following: Label Name Manufacturer Description AC1 Invisu™ 3100 Dow Chemical Co Acrylic polymer(1) AC2 Robond™ PS-7860 Dow Chemical Company Acrylic polymer(1) AC3 Robond™ PS-7874 Dow Chemical Company Acrylic polymer(1) RE1 Snowtack™ SE 782G Lawter Co. Rosin ester(2) (1) qualifies as (POLb) or (POLc1) (2) rosin ester is a tackifying agent and is not an acrylic polymer nfrRznn / zznz / E / viA The results of the loop-through tack test were as follows. Tack is the peak force described above, reported in Newtons (N). E.g. means Example. Example numbers ending in C are comparative. Comp. means composition. Coating weight means coating weight reported in grams of dry coating per square meter (gsm). Tack agent means rosin ester tack agent (in comparative examples) or acrylic polymer (POLc2) in the practical example. % tack agent is the percentage by weight of tack agent, based on the total dry weight of the bonded layer. Example 1 2C 3C 4C Lb: Comp. AC1 none AC2 none Lb: Coating weight (gsm) 20 0 20 0 Le: Comp. of POLc1 AC1 AC1 AC3 AC3 Le: Comp. of tackifier PE1 PE1 RE1 RE1 Le: % of tackifier 20 20 20 20 Le: Coating weight (gsm) 20 20 20 20 Tackiness (N) 5.4 5.8 6.9 9.0 The failure mode in all stickiness tests was adhesive failure (i.e., clean separation between the test substrate (Sd) and the pressure-sensitive article layer that was in contact with the substrate (Sd). SIMS result in Example 3C: the REI concentration was uniform throughout the depth. That is, the REI concentration was constant with depth along layers (Le) and (Lb). It is emphasized that although, when the layers were prepared, REI was present only in layer (Le) and not in layer (Lb), when the sample was analyzed, REI had diffused uniformly along layers (Lb) and (Le). SIMS results for Example 1: Layer (Le) showed a relatively high concentration of PEI, with only a slight decrease in concentration as the location approached the interface with layer (Lb). In layer (Lb), there was a more pronounced decrease in PEI concentration as the location moved from the interface between layers (Le) and (Lb) toward the substrate (Sa). In summary, there was a significantly higher concentration of PEI in layer (Le) than in layer (Lb). The confinement of PEI to layer (Le) is expected to promote good tack resistance in the pressure-sensitive article of the present invention. The SIMS results are consistent with the tackiness results. Comparing Comparative Example 4C with Comparative Example 3C, it is clear that when the tackifying agent can migrate freely through both layers (as shown in the SIMS data), reducing the tackifying agent concentration in the top layer results in a relatively large loss of tackiness performance: a drop from 9 Newtons to 6.9 Newtons (a 23% decrease in adhesion strength). In contrast, comparing Comparative Example 2C with Example 1, it is clear that when the migration of the tackifying agent is significantly inhibited, the drop in tackiness performance is also small: a drop from 5.8 Newtons to 5.4 Newtons (a decrease of only 7% in adhesion strength).In other words, when the tackifying agent does not migrate out of the top layer, the pressure-sensitive article retains its ability to exert a relatively high tackiness. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.< / tm>

Claims

1. A pressure-sensitive adhesive article characterized in that it comprises (a) a substrate (Sa), (b) in contact with the substrate (Sa), a layer (Lb) of a pressure-sensitive composition (Cb) comprising one or more acrylic polymers (POLb) having a Tg of 20°C or less, and (c) in contact with the layer (Lb), a layer (Le) comprising, by weight as a function of the weight of the layer (Le), (i) from 60% to 99.5% of one or more acrylic polymers (POLcl) having a Tg of 20°C or less, and (ii) from 0.5% to 40% of one or more acrylic polymers (POLc2) having a number-average molecular weight of 2,000 or greater, having a number-average molecular weight of 35,000 or less, having a Tg of -10°C or greater, and comprising polymerized units, by weight as a function of the weight of (POLc2), (A) from 50% to 99.(B) 9% of one or more unsubstituted alkyl esters of (meth)acrylic acid, wherein the alkyl group has from 1 to 20 carbon atoms, (C) 0% to 50% of acrylic acid, methacrylic acid or a mixture thereof, and 0% to 50% of one or more additional vinyl monomers.

2. The pressure-sensitive article according to claim 1, characterized in that the acrylic polymer (POLc2) was prepared by a process comprising aqueous emulsion polymerization of one or more monomers in the presence of the chain transfer agent in the amount of 1% to 10% by weight depending on the total weight of monomers.

3. The pressure-sensitive article according to claim 1, characterized in that the acrylic polymer (POLc2) comprises, by weight as a function of the weight of the acrylic polymer (POLc2), from 80% to 99.9% of polymerized units of one or more unsubstituted alkyl esters of (meth)acrylic acid, and from 0% to 20% of polymerized units of (meth)acrylic acid.

4. A method for preparing the pressure-sensitive article according to claim 1, characterized in that it comprises (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of the acrylic polymer (POLb) on a first surface, (B) forming a layer of an aqueous composition (Qc) containing dispersed particles containing (i) the acrylic polymer (POLcl) and (ii) the acrylic polymer (POLc2) on a second surface, (C) drying the layer of the aqueous composition (Qb) to form layer (Lb), and (D) drying the layer of the aqueous composition (Qc) to form layer (Le).

5. The method according to claim 4, characterized in that the aqueous composition (Qb) has been prepared by a process comprising the aqueous emulsion polymerization of one or more monomers to produce dispersed particles of the acrylic polymer (POLb).

6. An adhered article characterized in that it is manufactured by a process of bringing a substrate (Sd) into contact with the article according to claim 1, wherein the substrate (Sd) is in contact with the layer (Le).

7. The attached article according to claim 4, characterized in that the substrate (Sd) is a polyolefin.